Apparatus and method for interference mitigation

ABSTRACT

An apparatus in a wideband radio transceiver for mitigating interference between a wideband radio operating in a wide frequency band and a narrowband radio operating in a narrow frequency band within the wide frequency band. The effects of transmissions by the wideband radio on the narrowband radio are reduced by creating by the wideband radio, a transmitter notch of decreased transmit power centered at a frequency in the wide frequency band that is fixed in relation to the wideband carrier frequency. The wideband carrier frequency is then adjusted so that the transmitter notch is aligned with the second radio&#39;s narrow frequency band. The effects of transmissions by the narrowband radio on the wideband radio are reduced by creating by the wideband radio, a fixed receiver notch of decreased receiver gain in the wideband receiver, and aligning the narrowband signal with the fixed receiver notch.

RELATED APPLICATIONS

This application is a divisional application of a co-pending U.S. patentapplication Ser. No. 11/275,154 filed Dec. 15, 2005, which claims thebenefit of Provisional Application No. 60/723,041 filed Oct. 3, 2005,the entire disclosures of which are incorporated herein by reference.

BACKGROUND

The present invention relates to radio communication systems. Moreparticularly, and not by way of limitation, the present invention isdirected to an apparatus and method for mitigating interference betweenradio users operating in the same frequency band.

Radio operations have recently been allowed in the frequency range3.1-10.6 GHz. Instead of a fixed allocation of radio bands, the newradio transmissions will overlap with existing services. This isaccomplished by the use of so-called Ultra Wideband (UWB) modulationtechniques. A signal is denoted UWB when it either has a bandwidth of atleast 500 MHz, or has a fractional bandwidth larger than 0.2. Thetransmit power is spread over a large frequency range, resulting in alow power spectral density (PSD) which is measured in dBm/MHz. Theemission levels established by the FCC are rather low, resulting in asevere limitation of the range of UWB radio systems. UWB systems aretherefore typically used in short-range systems providing WirelessPersonal Area Networking (WPAN).

UWB emissions may interfere with the communication of other,narrower-band, systems operating in the 3.1-10.6 GHz band. However,these so-called victim systems have much narrower bandwidths, andtherefore will experience the UWB emission as an increase in the noisefloor. Systems that will be impacted by the UWB emission include FixedServices (Wireless Local Loop) operating around 3.4 GHz, Wireless LocalArea network (MAN) systems operating around 5 GHz, and envisionedcellular systems (beyond IMT-2000) that may operate at frequenciesbetween 3 and 6 GHz.

There are several occasions in which the increase in noise floor in thevictim receivers in not acceptable. When a mobile terminal is at a cellborder or finds itself under heavy fading conditions, it may operate atthe limit of its sensitivity. Any increase of the noise floor, caused bya UWB system, will result in an unacceptable performance degradation.Thus, in essence, the UWB emission reduces the range of the victimsystem. This range reduction can only be compensated for by using morebase stations, which is not a desirable solution.

Many UWB developers are, therefore, working on interference mitigationtechniques. Proposed solutions include having the UWB devices scan thefrequency spectrum of interest, and when they detect an existing system(for example a Worldwide Interoperability for Microwave Access (WiMAX)system at 3.41 GHz), they avoid that part of the spectrum. Thistechnique is called Detect-And-Avoid (DAA). Such avoidance, however, isnot a trivial task. Since the UWB transmission is very wide (0.5-1 GHz),a notch must be created within the transmit spectrum. In addition, thenotch must be deep enough (for example 30 dB or more) in order to limitthe UWB emission at the frequency to be avoided. Furthermore, thelocation of the notch must be variable since the victim carrierfrequency is not fixed.

The current UWB technologies can be divided into three classes:

a) Orthogonal Frequency Division Multiplexing (OFDM) based: this is anup-scaled OFDM technique with 128 sub-carriers and a carrier spacing of4.125 MHz, rendering a total bandwidth of 528 MHz.

b) Direct-Sequence Spread Spectrum (DSSS) based: this technique useschip rates on the order of 1-2 Gchips/s with variable spreading factors.

c) Pulse based: this technique uses very short pulses with a pulseduration that is a fraction of a nanosecond. Most pulse-based techniquesuse Pulse Position Modulation (PPM) to carry the information.

With the OFDM technique, variable notches with a depth of approximately20 dB can be obtained by inactivation of specific sub-carriers. Withmore advanced techniques (for example, using a dummy sub-carrier tocompensate), at most 30 dB can be obtained. In some cases, however,notches deeper than 30 dB may be required. For the DSSS and pulse-basedtechniques, variable notching is an even larger problem, making it muchmore difficult to obtain notch depths equivalent to those obtainablewith OFDM. Use of the DSSS and pulse-based techniques is desirable,however, because in contrast to OFDM-based UWB, use of these techniquesresults in very low implementation costs.

A method and apparatus for adapting multi-band UWB signaling tointerference sources is described in U.S. Patent Application PublicationNo. US 2004/0048574 (Walker et al.). However, Walker et al. do notdisclose or suggest any methodology utilizing notches in a UWB spectrumto mitigate interference.

Thus, what is needed in the art is an apparatus and method forinterference mitigation that overcomes the deficiencies of conventionalsystems and methods, and can be used with OFDM, DSSS, and pulse-basedUWB techniques. The present invention provides such an apparatus andmethod.

SUMMARY

Rather than attempting to vary the frequency of a notch within thetransmission frequency range of a UWB system to match the frequency ofan interfering narrowband system, the present invention forms a notch ata fixed position relative to the carrier frequency of the UWB system.The carrier frequency is then varied so as to superimpose the notch overthe frequency of the narrowband system. Such a fixed notch filter canobtain notch depths in excess of 30 dB. Therefore, the present inventioncan be used with all UWB technologies, including OFDM, DSSS, andpulse-based technologies.

Thus, in one aspect, the present invention is directed to a method ofmitigating interference between a first radio operating in a widefrequency band and a second radio operating in a narrow frequency bandwithin the wide frequency band. The method includes creating by thefirst radio, a transmitter notch of decreased transmit power centered ata selected frequency in the wide frequency band, wherein the selectedfrequency has a position in the wide frequency band that is fixed inrelation to a wideband carrier frequency. The method then adjusts thewideband carrier frequency so that the transmitter notch is aligned withthe second radio's narrow frequency band, thereby reducing interferencethat transmissions by the first radio cause for the second radio.

In another aspect, the present invention is directed to a method ofdecreasing interference on a radio operating in a wide frequency bandfrom a narrowband signal within the wide frequency band. The methodincludes creating by the wideband radio, a fixed receiver notch ofdecreased receiver gain in the radio's wideband receiver, and aligningthe narrowband signal with the fixed receiver notch. The aligning stepmay be accomplished by selecting a local oscillator (LO) frequency sothat when the narrowband signal is down-converted from radio frequency(RE) to intermediate frequency (IF), the narrowband signal is alignedwith the fixed receiver notch.

In another aspect, the present invention is directed to an apparatus ina wideband radio transceiver for mitigating interference between awideband radio operating in a wide frequency band and a narrowband radiooperating in a narrow frequency band within the wide frequency band. Theapparatus includes a fixed notch filter for creating a transmitter notchof decreased transmit power centered at a selected frequency in the widefrequency band. The selected frequency has a position in the widefrequency band that is fixed in relation to the wideband carrierfrequency. The apparatus also includes means for adjusting the widebandcarrier frequency so that the transmitter notch is aligned with thenarrowband radio's narrow frequency band, thereby reducing interferencethat transmissions by the wideband transceiver cause for the narrowbandradio.

In another aspect, the present invention is directed to an apparatus ina wideband radio transceiver for mitigating interference on a widebandradio operating in a wide frequency band from a narrowband signal withinthe wide frequency band. The apparatus includes a fixed notch filter forcreating a fixed receiver notch of decreased receiver gain in thewideband transceiver, and means for aligning the narrowband signal withthe fixed receiver notch. The means for aligning may include means forselecting an LO frequency such that when the narrowband signal isdown-converted from RF to IF, the narrowband signal is aligned with thefixed receiver notch.

In another aspect, the present invention is directed to a method ofmitigating interference between a first radio operating in a widefrequency band and a plurality of narrowband radios operating at aplurality of carrier frequencies within the wide frequency band. Themethod includes determining a frequency range that encompasses thecarrier frequencies of the plurality of narrowband radios; creating bythe first radio, a transmitter notch of decreased transmit powercentered at a notch frequency at a midpoint of the determined frequencyrange; and adjusting a transmitter notch bandwidth so that the bandwidthof the transmitter notch covers the determined frequency range.

In another aspect, the present invention is directed to a method ofmitigating interference between a wideband radio operating in a widefrequency band and a plurality of narrowband signals transmitted at aplurality of carrier frequencies within the wide frequency band. Themethod includes determining the carrier frequency of each of theplurality of narrowband signals; determining a signal power of each ofthe plurality of narrowband signals; determining a notch frequency bydetermining an average of the carrier frequencies of the plurality ofnarrowband signals weighted by the signal power of each of the pluralityof narrowband signals; and creating by the wideband radio, a receivernotch of decreased transmit power centered at the determined notchfrequency.

In another aspect, the present invention is directed to an apparatus ina wideband radio for mitigating interference between the wideband radioand a plurality of narrowband radio signals transmitted at a pluralityof carrier frequencies within the wideband radio's frequency band. Theapparatus includes means for determining a frequency range thatencompasses the carrier frequencies of the plurality of narrowbandsignals; a notch filter with a fixed notch frequency for creating atransmitter notch of decreased transmit power centered at a notchfrequency at a midpoint of the determined frequency range; and means foradjusting a transmitter notch bandwidth so that the bandwidth of thetransmitter notch covers the determined frequency range.

In another aspect, the present invention is directed to an apparatus ina wideband radio for mitigating interference between the wideband radioand a plurality of narrowband radio signals transmitted at a pluralityof carrier frequencies within the wideband radio's frequency band. Theapparatus includes means for determining the carrier frequency of eachof the plurality of narrowband signals; means for determining a signalpower of each of the plurality of narrowband signals; means fordetermining a notch frequency by determining an average of the carrierfrequencies of the plurality of narrowband signals weighted by thesignal power of each of the plurality of narrowband signals; and a notchfilter with a fixed notch frequency for creating a receiver notch ofdecreased receiver gain centered at the determined notch frequency.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following section, the invention will be described with referenceto exemplary embodiments illustrated in the figures, in which:

FIG. 1 is an illustrative drawing of a UWB transmitter spectrumoverlaying a narrowband Fixed Services (FS) transmitter spectrum;

FIG. 2 is an illustrative drawing of the UWB transmitter spectrum ofFIG. 1 overlaying the narrowband FS transmitter spectrum, and with anotch aligned with the FS frequency F₁;

FIG. 3 is an illustrative drawing of the UWB transmitter spectrum ofFIG. 1 overlaying the narrowband FS transmitter spectrum, and with thenotch aligned with a new FS frequency F₂;

FIG. 4 (Prior Art) is a simplified block diagram of a typical UWBtransceiver implemented with a variable transmitter notch filter;

FIG. 5 is an illustrative drawing of a UWB transmitter spectrum with afixed notch aligned with the UWB carrier frequency F₀ in accordance withthe teachings of the present invention;

FIG. 6 is an illustrative drawing of the UWB transmitter spectrum ofFIG. 5 with the fixed notch aligned with the UWB carrier frequency F₀,and with F₀ positioned at an FS frequency F₁ in accordance with theteachings of the present invention;

FIG. 7 is an illustrative drawing of the UWB transmitter spectrum ofFIG. 5 with the fixed notch aligned with the UWB carrier frequency F₀,and with F₀ positioned at an FS frequency F₂ in accordance with theteachings of the present invention;

FIG. 8 is a simplified block diagram of a first exemplary embodiment ofthe present invention in which a UWB transceiver is implemented withfixed notch filters in the transmitter stage and the receiver stage;

FIG. 9 is a simplified block diagram of a second exemplary embodiment ofthe present invention in which a UWB receiver is implemented with afixed notch filter for mitigating interference from a narrowband jammerwithin the UWB spectrum;

FIG. 10 is an illustrative drawing of a UWB receiver spectrum overlayinga narrowband FS jammer spectrum;

FIG. 11A is an illustrative drawing showing the (fixed) frequencyresponse H(f) of the notch filter in the receiver of FIG. 9, with thenotch at F_(notch);

FIG. 11B is an illustrative drawing showing the down-converted receivedsignal after the first mixer of the receiver of FIG. 9;

FIG. 11C is an illustrative drawing showing the resulting reduction ofthe jammer signal after filtering by the receiver of FIG. 9;

FIG. 12A is an illustrative drawing showing the (fixed) frequencyresponse H(f) of the notch filter in the receiver of FIG. 9, with thenotch at F_(notch), at the center of the UWB spectrum;

FIG. 12B is an illustrative drawing showing the down-converted receivedsignal after the first mixer, with the UWB spectrum centered onF_(notch) and wherein F₀=F₁=F_(notch);

FIG. 12C is an illustrative drawing showing the resulting reduction ofthe jammer signal after filtering by the receiver of FIG. 9, with theUWB spectrum centered on F_(notch) and wherein F₀=F₁=F_(notch);

FIG. 13 is a flow chart illustrating the steps of an embodiment of themethod of the present invention when a single narrowband interferingsignal is found within the UWB receiver spectrum;

FIG. 14 is an illustrative drawing of a UWB receiver spectrum overlayingmultiple narrowband interfering signals;

FIG. 15 is a flow chart illustrating the steps of an embodiment of themethod of the present invention when multiple narrowband interferingsignals are found at different frequencies within the UWB spectrum; and

FIG. 16 is an illustrative drawing of three narrowband interferingsignals of unequal strength within the UWB spectrum.

DETAILED DESCRIPTION

As noted above, making a notch at a variable frequency in the transmitspectrum of a UWB radio system, particularly a DSSS or pulse-basedsystem, is a problem. Therefore, the present invention creates a notchat a frequency fixed in relation to the carrier frequency of the UWBsystem, and varies the carrier frequency instead to align the notch withthe transmission frequency of the victim system. Since UWB devices aretypically used for unlicensed, short-range use, in most situations onlya single UWB channel is present. Coordination between multiple UWBchannels is not required, because UWB units in range will most likelyjoin the same channel. This obviates the need for a fixed carrierallocation. UWB devices can find each other by starting at one (orseveral) a priori known, fixed carrier frequency. However, after the DAAprocedure, a notch is created in the spectrum and the total transmissionspectrum is shifted so that the notch is aligned with the victimfrequency.

The present invention minimizes the interference between the UWBtransmitter and the victim receiver, as well as the interference betweenthe victim transmitter and the UWB receiver. Like the UWB transmitter,the UWB receiver effectively notches out a fixed part of the receivedsignal. Therefore, the required dynamic range of the UWB receiver isreduced because it does not have to deal with the strong signals fromthe victim transmitter.

FIG. 1 is an illustrative drawing of a UWB transmitter spectrum 11overlaying a narrowband Fixed Services (FS) transmitter spectrum 12. UWBradio communications utilize an extremely large bandwidth, in the orderof 0.5-2 GHz. Thus with high probability, the UWB transmission willoverlap with a narrowband radio signal such as the FS service spectrum.The UWB transmission is centered at F₀ whereas the FS transmission iscentered at F₁. When in close range, the UWB emission will degrade theperformance of the FS receiver. Conversely, in the UWB receiver stage,the FS transmitter may also interfere with or jam the UWB receiver.

FIG. 2 is an illustrative drawing of the UWB transmitter spectrum 11overlaying the narrowband FS transmitter spectrum 12, and with a notch13 aligned with the FS frequency F₁. For optimal coexistence, the UWBspectrum and the FS spectrum should be mutually exclusive. FIG. 2 showshow the UWB system has created a notch in the transmit spectrum aroundF₁ in order to permit an interference-free band for the FS system.

FIG. 3 is an illustrative drawing of the UWB transmitter spectrum 11overlaying the narrowband FS transmitter spectrum 12, and with the notch13 aligned with a new FS frequency F₂. Since the FS signal may switchfrom F₁ to F₂, the notch carrier frequency F_(notch) must be variable inorder to permit an interference-free band for the varying FS system. Inpractice, however, creation of a variable F_(notch) is highlyproblematic. Variable notch filters are costly, difficult to achievewith on-chip components, and do not render deep notches of 30 dB or morewithout suppressing a large part of the received signal bandwidth.

FIG. 4 is a simplified block diagram of a typical UWB transceiver 20implemented with a variable transmitter notch filter 21. The transceiverincludes a transmitter stage 22 and a receiver stage 23. The transmitterstage includes a modulator 24, the variable notch filter 21, an upconverter 25 connected to a synthesizer 26 for conversion from anintermediate frequency (IF) to RF, and a power amplifier 27. Preferably,the variable notch filter is built at the IF stage or at base bandbecause it is not practical to build a variable notch filter at RF. Inthis embodiment, the receiver stage 23 is a conventional UWB receiverstage having a low noise amplifier (LNA) 28, a down converter 29connected to the synthesizer 26, and a demodulator 30.

FIG. 5 is an illustrative drawing of a UWB transmitter spectrum 31 witha fixed notch 32 aligned with the UWB carrier frequency F₀ in accordancewith the teachings of the present invention. Because of the difficultiesin implementing a variable notch filter, the present invention utilizesa fixed notch carrier instead. Preferably, the notch is in the middle ofthe spectrum as is shown in FIG. 5, but any other fixed location(relative to the UWB carrier frequency F₀) may also be utilized. Such anotch may be created in the transmitter stage, for example, by ahigh-pass filter at base band. Alternatively, the notch may be createdby a (fixed) high-Q filter at IF. The base band or IF signal is thenup-converted to RF utilizing an LO frequency such that the resultingnotch frequency F_(notch) coincides with the victim carrier frequency.

FIG. 6 is an illustrative drawing of the UWB transmitter spectrum 31with the fixed notch 32 aligned with the UWB carrier frequency F₀, andwith F₀ positioned at F₁, the frequency of a narrowband FS spectrum 33,in accordance with the teachings of the present invention. Thus, in thisexample, the notch frequency F_(notch) is identical to the UWB centerfrequency F₀, and the victim system spectrum 33 is centered at F₁. Whenthe UWB centre frequency is placed at F₁, then F_(notch)=F₀=F₁, and aninterference-free band for the FS system is created at F₁.

FIG. 7 is an illustrative drawing of the UWB transmitter spectrum 31with the fixed notch 32 aligned with the UWB carrier frequency F₀, andwith F₀ positioned at an FS frequency F₂, in accordance with theteachings of the present invention. Thus, in this example, the notchfrequency F_(notch) is identical to the UWB center frequency F₀, and thevictim system spectrum 33 is centered at F₂. When the UWB centrefrequency is placed at F₂, then F_(notch)=F₀=F₂, and aninterference-free band for the FS system is created at F₂.

FIG. 8 is a simplified block diagram of a first exemplary embodiment ofthe present invention in which a UWB transceiver 40 is implemented witha fixed notch filter 41 in the transmitter stage 42, and a fixed notchfilter 43 in the receiver stage 44. The transmitter stage includes amodulator 45, the fixed transmitter notch filter 41, an up converter 46connected to a synthesizer 47 for conversion from IF to RF, and a poweramplifier 48. Preferably, the fixed notch filter 41 is built at the IFstage or at base band. In this embodiment, the receiver stage 44 hasalso been implemented with a fixed notch filter 43 in order to reducethe FS signal that interferes with or jams the UWB received signal.Thus, the receiver stage includes an LNA 49, a down converter 50connected to the synthesizer 47, the receiver fixed notch filter 43, anda demodulator 51.

Since the notch filters in FIG. 8 are fixed, such filters can easily berealized with depths of 30 dB or more. Note that the notch filters arefixed implementations and do not need variable notch carriers as was thecase in the implementation shown in FIG. 4. The up-conversion anddown-conversion takes care of the alignment of the notch with the victimfrequency. Note that the notch filters 41 and 43 may still beconfigurable. However, it is not the notch carrier frequency, but ratherthe notch bandwidth that may be variable. The latter is simpler toachieve than changing the carrier. The notch bandwidth may be varied,depending on the width of the frequency band to be avoided.

FIG. 9 is a simplified block diagram of a second exemplary embodiment ofthe present invention in which an exemplary UWB receiver 60 isimplemented with a fixed notch filter 61 for mitigating interferencefrom a narrowband jammer within the UWB spectrum. The filter 61 has afixed notch at F_(notch). In the embodiment described above, both theUWB transmitter and the UWB receiver are re-tuned to a new carrierfrequency. In the embodiment illustrated in FIG. 9, the RF frequency ischanged only in the UWB receiver. This approach reduces the interferenceof a narrowband jammer in the UWB receiver, but does not suppressinterference in the narrowband system resulting from the UWBtransmissions.

FIG. 10 is an illustrative drawing of a UWB receiver spectrum 71overlaying a narrowband FS jammer spectrum 72. As is shown, the jammeris not at the UWB center frequency F₀ as would be configured with theprevious embodiment, but at some frequency F₁>F₀.

In the receiver embodiment shown in FIG. 9, the local oscillator (LO)frequency F_LO of the first mixer in the UWB receiver is tuned such thatthe jammer frequency F₁ is aligned with the fixed (IF) notch frequency.After the first mixer stage at 62, the RF signal is down-converted at 63to an IF frequency (or to complex base band). However, instead ofselecting an LO frequency to down-convert the UWB center frequency to anappropriate IF frequency, the LO frequency is selected to down-convertthe jammer frequency F₁, and align F₁ with the fixed notch frequencyF_(notch). Thus, F_LO=F₁−F_(notch). In a second down-conversion stage(not shown), the signal (with suppressed jammer) may be converted to anIF, which is more suitable for carrying out functions such as channelfiltering. This may also be done in the digital domain. Since the jammerhas been suppressed by the notch filter, the dynamic range of the signalis reduced, and the requirements on the analog-to-digital converters(ADCs) are relaxed. After applying the fixed notch filter 61, thereceived signal is passed to a demodulator 64.

FIGS. 11A-11C illustrate the effect of the receiver architecture of FIG.9 on a narrowband jammer signal 72. FIG. 11A is an illustrative drawingshowing the (fixed) frequency response H(f) of the notch filter 61 inthe receiver of FIG. 9, with the notch 73 at F_(notch). FIG. 11B is anillustrative drawing showing the down-converted received signal afterthe first mixer. Finally, FIG. 11C is an illustrative drawing showingthe resulting reduction of the jammer signal after filtering by thereceiver of FIG. 9.

In the embodiment of FIGS. 9-11, it may be advantageous to have thenotch frequency in the center of the UWB spectrum. In that way, thenotch filtering can easily be combined with channel filtering. Also,when using base band processing, the notch filter can be realized with ahigh-pass filter. Thus, a third embodiment of the present inventioncombines aspects of the first and second embodiments above. In thisembodiment, notch filtering is only applied in the receiver (as in thesecond embodiment). The LO in the receiver 60 (FIG. 9) makes sure thejammer center frequency F₁ coincides with the notch frequency F_(notch).In addition, the receiver may also order the transmitter to center itscarrier frequency F₀ on the notch frequency F_(notch) (as in the firstembodiment), where F_(notch)=F₁, the narrowband jammer carrierfrequency.

FIG. 12A is an illustrative drawing showing the (fixed) frequencyresponse H(f) of the notch filter 61 in the receiver of FIG. 9, with thenotch at F_(notch), at the center of the UWB spectrum. FIG. 12B is anillustrative drawing showing the down-converted received signal afterthe first mixer, with the UWB spectrum centered on F_(notch) and whereinF₀=F₁=F_(notch). Finally, FIG. 12C is an illustrative drawing showingthe resulting reduction of the jammer signal 72 after filtering by thereceiver of FIG. 9, with the UWB spectrum centered on F_(notch) andwherein F₀=F₁=F_(notch).

In the present invention, the notch frequency F_(notch) in the UWBtransmit spectrum is aligned with the narrowband jammer frequency F₁. Tofind the jammer frequency, the transceiver first has to scan thespectrum for energy. The scanning may be carried out by one or bymultiple transceivers. When multiple transceivers are utilized, thefindings are forwarded to a single master unit. The transceivers maycommunicate with the master unit in a conventional manner. Extrarobustness may be applied (for example, retransmissions, Forward ErrorCorrection (FEC) coding, low rate modulation, and the like) to reducethe impact of the jammer.

FIG. 13 is a flow chart illustrating the steps of an embodiment of themethod of the present invention when a single narrowband interferingsignal is found within the UWB spectrum. At step 81, one or more UWBtransceivers scan the UWB spectrum for energy. The energy measurementsmay be sent to a master unit, which determines at step 82 whether anarrowband interfering signal was found. If not, the method moves tostep 83 and keeps the current LO settings. However, if a narrowbandinterfering signal was found, the method moves to step 84 where the LOsettings are adjusted such that F_(notch)=F₁. The LO setting in the UWBtransmitter may be adjusted so that UWB transmissions do not interferewith the narrowband user. Likewise, the LO setting in the UWB receivermay be adjusted so that transmissions by the narrowband user do notinterfere with the UWB receiver. Thus, at step 85, communicationscontinue by both the UWB user and the narrowband user without any, orwith greatly reduced, mutual interference.

The situation may also arise in which multiple narrowband interferingsignals are found at different frequencies within the UWB spectrum. Ascenario showing three such interfering signals is illustrated in FIG.14. In this scenario, the three interfering signals are of approximatelyequal magnitude, but are not evenly spaced in the frequency spectrum.The three signals are bounded at the lower end by frequency F_(L) and atthe upper end by frequency F_(U).

FIG. 15 is a flow chart illustrating the steps of an embodiment of thepresent invention when multiple narrowband interfering signals are foundat different frequencies within the UWB spectrum. At step 91, one ormore UWB transceivers scan the UWB spectrum for energy. The energymeasurements may be sent to a master unit, which determines at step 92whether multiple narrowband interfering signals were found. If not, themethod moves to step 93 and determines whether a single interferingsignal was found. If no interfering signals were found, the method movesto step 94 and keeps the current LO settings. Communications thencontinue at step 102. However, if a single narrowband interfering signalwas found, the method moves to step 95 where the LO settings areadjusted such that F_(notch)=F₁. Communications then continue at step102.

If it was determined at step 92 that multiple narrowband interferingsignals were found, the method moves to step 96 where a lower frequencyboundary F_(L) and an upper frequency boundary F_(U) are determined. Atstep 97, it is determined whether the notch bandwidth can be adapted. Ifso, the method moves to step 98 where the notch bandwidth is adjusted toequal the range from F_(L) to F_(U) (i.e., BW_(notch)=(F_(U)−F_(L)). Atstep 99, the notch is set up at the midpoint between F_(L) and F_(U) byadjusting the transmit and receive LO settings such that:

$F_{notch} = {\frac{F_{U} + F_{L}}{2}.}$Communications then continue at step 102. However, if it is determinedat step 97 that the notch bandwidth cannot be adapted, the presentinvention moves to step 100 where it is determined whether theinterferers have approximately equal signal strength.

Referring briefly to FIG. 16, a scenario is illustrated in which threenarrowband interfering signals of unequal strength are found within theUWB spectrum. Signals A, B, and C are shown to be at carrier frequenciesF_(A), F_(B), and F_(C), and have power levels at P_(A), P_(B), andP_(C), respectively.

Referring again to FIG. 15, if the interferers have approximately equalsignal strength at step 100, the method moves to step 99 and sets thenotch frequency F_(notch), at the midpoint between F_(L) and F_(U).Communications then continue at step 102. However, if the interferers donot have approximately equal signal strength, the method moves insteadto step 101 and skews the notch frequency towards the stronger jammersby weighting each of the narrowband carrier frequencies with thereceived signal power of each signal. Thus, in the example of FIG. 16:

${Fnotch} = \frac{{P_{A}F_{A}} + {P_{B}F_{B}} + {P_{C}F_{C}}}{P_{A} + P_{B} + P_{C}}$For N jammers, this can be generalized to:

${Fnotch} = \frac{\overset{N}{\sum\limits_{i = 1}}{P_{i}F_{i}}}{\overset{N}{\sum\limits_{i = 1}}P_{i}}$

Thus, for the example shown in FIG. 16, F_(notch) will not be half waybetween F_(U) and F_(L), but will be closer to F_(B). In case noindividual jammer frequencies F_(A), F_(B), . . . can be identified, thenotch frequency can also be determined by:

${Fnotch} = \frac{\int_{FL}^{F_{U}}{{f \cdot {P(f)}}{\mathbb{d}f}}}{\int_{FL}^{F_{U}}{{P(f)}{\mathbb{d}f}}}$At step 102, communications continue by the UWB user and the narrowbandusers without any, or with greatly reduced, mutual interference.

As described herein, the present invention provides efficient, low-cost,and low-power interference mitigation techniques. The inventionadditionally provides high performance with deep notch filters. Theinvention not only reduces interference to incumbent radio systems, butalso improves the reception of UWB signals.

As will be recognized by those skilled in the art, the innovativeconcepts described in the present application can be modified and variedover a wide range of applications. Accordingly, the scope of patentedsubject matter should not be limited to any of the specific exemplaryteachings discussed above, but is instead defined by the followingclaims.

As will be recognized by those skilled in the art, the innovativeconcepts described in the present application can be modified and variedover a wide range of applications. Accordingly, the scope of patentedsubject matter should not be limited to any of the specific exemplaryteachings discussed above, but is instead defined by the followingclaims.

What is claimed is:
 1. A method of decreasing interference in a radionetwork in which a wideband radio transmits and receives a widebandsignal in a wide frequency band and a narrowband radio transmits andreceives a narrowband signal within the wide frequency band, said methodcomprising: decreasing interference to the wideband radio caused by thenarrowband signal by performing in a receiver of the wideband radio, thefollowing steps: creating by the wideband radio, a fixed receiver notchof decreased receiver gain at a selected frequency in the widebandradio's wideband receiver; and utilizing a local oscillator (LO)frequency such that when the narrowband radio's narrowband signal isdown-converted from radio frequency (RF) to intermediate frequency (IF),the narrowband radio's down-converted signal is aligned with thefrequency of the receiver notch; and decreasing interference to thenarrowband radio caused by the wideband signal by performing in thewideband radio, the following steps: reporting by the wideband receiverto a wideband transmitter, the fixed receiver notch frequency; andcentering the wideband transmitter's carrier frequency on the fixedreceiver notch frequency to reduce interference to the narrowband radio.2. In a wideband radio that transmits and receives a wideband signal ina wide frequency band, an apparatus for mitigating interference to andfrom a narrowband radio transmitting a narrowband signal within the widefrequency band, said apparatus comprising: a first circuit configured todecrease interference to the wideband radio caused by the narrowbandsignal, the first circuit comprising: a notch filter with a fixed notchfrequency for creating a fixed receiver notch of decreased receivergain; and a local oscillator (LO) set to a frequency such that when thenarrowband signal is down-converted from radio frequency (RF) tointermediate frequency (IF), the down-converted signal is aligned withthe frequency of the receiver notch; and a second circuit configured todecrease interference to the narrowband radio caused by the widebandsignal, wherein the second circuit is configured to: report to awideband radio transmitter, the fixed receiver notch frequency; andcenter the wideband transmitter's carrier frequency on the fixedreceiver notch frequency to reduce interference to the narrowband radio.3. A method of mitigating interference between a wideband radiooperating in a wide frequency band and a plurality of narrowband signalstransmitted at a plurality of carrier frequencies within the widefrequency band, said method comprising: mitigating interference to theplurality of narrowband signals caused by transmissions from thewideband radio by performing the steps of: determining a frequency rangethat encompasses the carrier frequencies of the plurality of narrowbandsignals; creating by the wideband radio, a transmitter notch ofdecreased transmit power centered at a notch frequency at a midpoint ofthe determined frequency range; and adjusting a transmitter notchbandwidth so that the bandwidth of the transmitter notch covers thedetermined frequency range; and mitigating interference to the widebandradio caused by transmissions from the plurality of narrowband signalsby performing the steps of: creating by the wideband radio, a receivernotch of decreased receiver gain centered at the notch frequency; andadjusting a receiver notch bandwidth so that the bandwidth of thereceiver notch covers the determined frequency range.
 4. In a widebandradio operating in a wide frequency band, an apparatus for mitigatinginterference between the wideband radio and a plurality of narrowbandradio signals transmitted at a plurality of carrier frequencies withinthe wide frequency band, said apparatus comprising: means for mitigatinginterference to the plurality of narrowband signals caused bytransmissions from the wideband radio, comprising: means for determininga frequency range that encompasses the carrier frequencies of theplurality of narrowband signals; a notch filter with a fixed notchfrequency for creating a transmitter notch of decreased transmit powercentered at a notch frequency at a midpoint of the determined frequencyrange; and means for adjusting a transmitter notch bandwidth so that thebandwidth of the transmitter notch covers the determined frequencyrange; and means for mitigating interference to the wideband radiocaused by transmissions from the plurality of narrowband signals,comprising: a second notch filter with a fixed notch frequency forcreating by the wideband radio, a receiver notch of decreased receivergain centered at the notch frequency; and means for adjusting a receivernotch bandwidth so that the bandwidth of the receiver notch covers thedetermined frequency range.